2015 MacBook Pro rapidly losing storage after deleting files

2015 Macbook Pro keeps running out of storage space - goes from 19 or so gig down to MBs in a 2-3 hours no matter what I'm doing even if its just surfing, working on a google doc or spreadsheet, writing an email.. It's so bad I haven't been able to update iOS since Catalina 10.15.7. There are several issues here that I think are all related but I don't know how to solve them: I've been deleting apps, files, pictures, etc, things are stored in icloud, icloud archive, drop box and google. Even though I'm deleting things, as I'm deleting them then emptying the trash, I'm still losing storage as I'm deleting. Sometimes in that process, files are duplicating themselves. I'd brought the laptop into the apple store where I was told there is nothing wrong with the files themselves and there are malware, viruses, or worms issues. Sometimes I've dragged some files to my external hard drive, but when I've tried to put them back on my laptop, I get the message my file is corrupted even though, the file was made with the current versions of the different apps and ios. The files are a mess and I don't know how to clean them up expeditiously. I end up losing my place as to where I've gotten up to in the process. And if I have the same file in different locations, which I'm not even sure how some of them go to where they end up, I don't know which files I should delete/save (archived, drive, dropbox or google files)